C#: Check whether a given number is prime or not

Last update on December 20 2024 12:41:02 (UTC/GMT +8 hours)

Write a C# Sharp Program to determine whether a given number is prime or not.

Visual Presentation:

Sample Solution:

C# Sharp Code:

using System;  // Importing necessary namespace

public class Exercise32  // Declaration of the Exercise32 class
{  
    public static void Main()  // Main method, entry point of the program
    {
        int num, i, ctr = 0;  // Declaration of variables num, i, and ctr as integers

        Console.Write("\n\n");  // Displaying new lines
        Console.Write("Check whether a given number is prime or not:\n");  // Displaying the purpose of the program
        Console.Write("-----------------------------------------------");  // Displaying a separator
        Console.Write("\n\n");  // Displaying new lines

        Console.Write("Input a number: ");  // Prompting the user to input a number
        num = Convert.ToInt32(Console.ReadLine());  // Reading the number entered by the user

        // Loop to check if the number is prime
        for (i = 2; i <= num / 2; i++)
        {
            if (num % i == 0)
            {
                ctr++;  // Incrementing the counter if the number has divisors other than 1 and itself
                break;  // Exiting the loop if a divisor is found
            }
        }

        // Checking the value of ctr to determine if the number is prime or not
        if (ctr == 0 && num != 1)
        {
            Console.Write("{0} is a prime number.\n", num);  // Displaying if the number is prime
        }
        else
        {
            Console.Write("{0} is not a prime number\n", num);  // Displaying if the number is not prime
        }
    } 
}

Sample Output:

Check whether a given number is prime or not:                                                                                         
-----------------------------------------------                                                                                                         
Input  a number: 53                                                                                                         
53 is a prime number. 

Flowchart:

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